1. Field of the Invention
This invention relates generally to forming contoured tubing and more particularly to contouring tubular stock in such a manner to maintain substantially uniform wall thickness so that the strength of the contoured tube is not effected.
2. Description of the Prior Art
Conventional techniques for forming tubing of variable cross-sectional contours include liquid bulging, electrohydraulic forming, and rubber punch bulging. These techniques are described in U.S. Pat. No. 3,520,163, issued Nov. 24, 1967 in the name of Otoda. Basically, in each technique, expansive forces are utilized to move tubular material into a mold or die having a complimentary surface to the desired finished tubular contour. A fourth technique for forming tubing involves the use of magnetic force fields to change the contour of tubular stock.
Of the known methods for contouring tubing, the simplest, in terms of necessary equipment, is rubber punch bulging. A solid ram is utilized to act on a rubber workpiece and thus the problems associated in working with hydraulic fluids under pressure are eliminated. Further the rubber workpiece, if properly selected, will return to its original shape to facilitate its removal from the contoured tubular shape. One drawback of rubber workpieces is that at the extreme pressures necessary to shape tubing, enough heat is generated to cause rapid deterioration of the rubber material. For this reason, polyurethane has been successfully used as a workpiece in place of rubber; see U.S. Pat. No. 3,670,545 issued June 20, 1972 in the name of Kent, et al.
In all of the above methods for forming contoured tubing, the wall thickness of the tube is altered thereby effecting the strength characteristics of the contoured tube. It is therefore important to control the forces being applied to contour the tube so as not to exceed the elongation factor of the tube material. If the elongation factor is exceeded substantial weakening of the material or, ultimately, tube rupture will occur.